Show how long Linux/MacOS system has been running after power on

uptime

 8:40  up 96 days, 21:39, 5 users, load averages: 21.65 84.31 65.51

uptime

This is the same information contained in the header line displayed by w(1).

System load averages is the average number of processes that are either in a runnable or uninterruptable state. A process in a runnable state is either using the CPU or waiting to use the CPU. A process in uninterruptable state is waiting for some I/O access, eg waiting for disk. The averages are taken over the three time intervals. Load averages are not normalized for the number of CPUs in a system, so a load average of 1 means a single CPU system is loaded all the time while on a 4 CPU system it means it was idle 75% of the time.